1. Field of the Invention
The application relates to a method utilized in a wireless communication system, and more particularly, to a method for canceling a call initiation in radio access technology change in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
Moreover, inter-radio access technology (inter-RAT) mobility involves transfer of a connection or mobility between a UE and a network from one RAT (e.g. the LTE system) to another RAT, such as Global System for Mobile communications (GSM)/Global Packet Radio Service (GPRS), Universal Mobile Telecommunications System (UMTS), or Code Division Multiple Access (CDMA) system. However, the applicant notices that a UE may encounter problems associated to the inter-RAT change as below based on a direct image on a basis of the prior art LTE system and UMTS system.
For example, a UE in the LTE system initiates a cell by circuit-switched fallback (CS fallback). The CS fallback capable UE supports access to E-UTRAN as well as access to the CS domain over UTRAN. The UE may receive a command from the E-UTRAN, e.g. a RRC connection release message or mobility from EUTRA command (containing cell change order), which redirects the UE to the UTRAN. Before the call is established successfully, the UE cancels initiating the call. In this situation, the UE can only clear the call by sending a DISCONNECT message for call clearing, as specified in section 5.4.3 of 3GPP TS 24.008. However, the DISCONNECT message can only be sent after the UE establishes the connection with the UTRAN. An establishment of the connection takes time and consumes transmission power.